1. Field of the Invention
The present invention relates to an optical-to-electrical converter unit and a semiconductor light-receiving device.
2. Description of the Related Art
In recent years, waveguide-type semiconductor light-receiving devices in which photodiodes and optical waveguides are integrated on semiconductor substrates have been studied. Such semiconductor light-receiving devices have high frequency characteristics which make them capable of responding to optical signals having high bit rates such as 40 Gb/s or higher, for example. Because of the high frequency characteristics, they are used as receiver front ends of optical transmission systems combining multi-level light intensity modulation systems and digital coherent receiving systems. The semiconductor light-receiving device is fabricated by forming, on a semiconductor substrate, a butt-joint structure including a stacked semiconductor layer section that constitutes a photodiode including an optical absorption layer and a stacked semiconductor layer section that constitutes an optical waveguide including a core layer.
Japanese Unexamined Patent Application Publication No. 2007-180425 (hereinafter referred to as '425 document) describes an optical semiconductor device. This optical semiconductor device includes a substrate in which a capacitor, a photodiode, and an electrode pad are arranged in particular regions. The capacitor and the electrode pad are arranged on the substrate so that the respective sides thereof are adjacent to each other with particular gaps therebetween.